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我們按照初中課本上册第165页所指示的步骤测定水的汽化熱,實驗過三次,但每次所求得的水的汽化熱仅得400卡/克左右,誤差很大。经过详细的研究,發現課本上所提出的實驗方法是有錯誤的。根据課本的步驟,要求出水在沸腾時間所吸收的熱量,先要算出每分钟水吸收的熱量的平均值,然後用這個平均值乘上沸腾的時間——即5分鐘。 伹是計算有多少水變成了蒸汽時,却是根据加熱前後水的質量的差來計算。事實上,由開始加熱到水沸腾之前,已經有相當質量的水蒸發掉了,特别是當水的温度接近沸點時蒸發得很快。因此,加熱前後水的質量的差不祇包含了在五分鐘沸腾期間汽化的水的質量,而且也包含了水由50℃到沸腾前所蒸發的水的質
We measured the heat of vaporization of water three times according to the procedure indicated on page 165 of the Junior High School Textbook, but the water vaporization heat obtained at each time was only about 400 calories / gram with a great error. After a detailed study, I found that the experimental method proposed in the textbook is wrong. According to the textbook procedure, the amount of heat absorbed by the effluent during the boiling time is calculated by averaging the amount of heat absorbed by the water per minute, and then multiplying it by the mean time of boiling - that is, 5 minutes.伹 is calculated how much water turns into steam, but it is based on the difference between the quality of water before and after heating to calculate. In fact, a considerable amount of water has evaporated before it starts to heat up, especially when the temperature of the water is near the boiling point. Therefore, the difference in mass of water before and after heating not only includes the mass of water vaporized during the five-minute boiling but also the mass of water that is evaporated from 50 ° C. to boiling